weak reverse after TCI 221500 transbrake install

[ccrp]

Hello all,

I have a customer tranny which got rebuild and upgraded with an TCI t-brake kit like many dozen others.

this one doesn't seem to have proper reverse, air pressue checks when it was build were all OK.

the way it feels is like very weak reverse (when in neutral + t-brake) and no t-brake function when in first. Works beautifully in all forward gears so pressure is there.

tried to rev it in neutral if it may have a stuck forward clutch pack but that is fine too, it is not driving off in neutral like it would when clutch clearance is too tight.

took solenoid out to see if plunger/control valve is sticking which it doesn't, check reverse piston and all looks good too.

any ideas what I could check?

[TCITech1]

If the rev band is air checking there has to be something wrong with the valvebody. Do you have another valvebody to try, if not send that one back to us so we can check it out. When you take the vb off look at the gaskets and make sure they are not blocking any holes the the plate, I have seen this happen before.

[AlkyV6]

I am in the exact same situation. I have triple checked the hydraulic circuits in the transmission and they have all checked out perfectly. I know that in a manual transbrake valvebody not much can go wrong so I've pulled my hair out with this problem before I finally came to the conclusion that it has to be the valve body.
I've traced the hydraulic circuitry of the valvebody and find that direct oil is being partially dumped at the back of the manual valve when the manual valve is in the reverse position. I don't understand why that would be. Am I reading this circuit correctly? I've gone over it countless times and keep coming up with the same conclusion.
Also, the rear servo is getting feed oil anytime that direct oil is supplied to the direct drum. That would seem fine for reverse and when on the transbrake, but how does this work in 3rd gear position? Wouldn't the reverse band apply in 3rd? I don't think we really would want that.
Please explain how the reverse servo is denied oil in 3 position, and why the large dump of 3rd gear oil in the reverse position.
Did something fall out of the valvebody during cleaning that I may not be aware of? There is one installed aluminum wall, or blockoff, in this valvebody I am working on. Should there be more? Did another one fall out, maybe?
I never removed any valves when I cleaned this valvebody except the custom manual valve. All blocking roll pins are in place.

[AlkyV6]

Is it possible the wrong manual valve was sent with this valvebody? The valve in this case is 4 5/8" long. I would think the valve should have a longer section at the back end to block the hemorrhaging of third gear oil in the reverse position. Say like a 6" long valve?

[TCITech1]

If high gear operates correctly and the transbrake won't hold and slips in reverse, then either something is wrong with the low/reverse band or servo assembly. Servo pin too short, missing/cut seal or missing servo cover gasket. 2nd gear oil keeps the low/reverse band from applying in 2nd and 3rd gears. The transbrake button must be activated in neutral to back up and prevent low pressure.